File:ISS-31 Linear dunes in the Great Sand Sea in southwest Egypt.jpg

Summary

Description	English: Linear dunes in the Great Sand Sea in southwest Egypt are featured in this image photographed by an Expedition 31 crew member on the International Space Station. In southwestern Egypt, deep in the Sahara Desert, the action of wind dominates landscapes today much as it has done for the past several thousand years. Winds blowing from the north have fashioned sands into large dunes, aligned parallel with these winds. The so-called linear dunes - shown here in the Great Sand Sea - are easily seen from space and local maps show that they rise 20--30 meters above the surrounding flat plains. The distance between individual linear dunes is interestingly regular, at 1.5--2.5 kilometers, suggesting some equilibrium exists between the formative wind strength and the sand supply. It is possible that linear dunes may relate to earlier times when winds were stronger than they are today, or sand more plentiful. The dark patch of rock outcrop at upper right sticks up above the surface on which the dunes lie by as much as 150 meters. The north winds have been deflected around this high zone, and smaller secondary linear dunes can be seen along the right side of the image, aligned with local winds that become ever more northeasterly with nearness to the outcrops. A dune-free zone on the protected downwind (south-southeast) side of the outcrop gives a sense of the sand movement (generally from the bottom of the image towards the top). At first glance, the large linear dunes appear to be the major landform in the image; however a complex pattern of even smaller dunes can be seen perched on top of the largest dunes (inset). The sand that comprises many dune fields usually, according to scientists, derives from some larger river not very distant upwind, supplied from the dry river bed (exposed to the wind during dry seasons of low river flow, or regional change to a more arid climate). Inland dune fields thus lie downwind of the source river. A large, unnamed river once flowed to the Mediterranean Sea situated west of the dunes shown in this picture, dumping its sand load 300 kilometers northwest of the area shown. It is likely that this river, the evidence of which is now almost completely obliterated, was the source of the sand in the linear dunes, the scientists say.
Date	11 May 2012
Source	http://spaceflight.nasa.gov/gallery/images/station/crew-31/html/iss031e030783.html
Author	NASA

This image or video was catalogued by Johnson Space Center of the United States National Aeronautics and Space Administration (NASA) under Photo ID: ISS031-E-030783.

This tag does not indicate the copyright status of the attached work. A normal copyright tag is still required. See Commons:Licensing.

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Licensing

This file is in the public domain in the United States because it was created by the Image Science & Analysis Laboratory, of the NASA Johnson Space Center. NASA copyright policy states that "NASA material is not protected by copyright unless noted". (NASA media use guidelines or Conditions of Use of Astronaut Photographs). Photo source: ISS031-E-30783.

Camera manufacturer	NIKON CORPORATION
Camera model	NIKON D2Xs
Exposure time	1/8,000 sec (0.000125)
F-number	f/4
ISO speed rating	400
Date and time of data generation	04:58, 11 May 2012
Lens focal length	180 mm
User comments	1137 76.1F
Orientation	Normal
Horizontal resolution	300 dpi
Vertical resolution	300 dpi
Software used	Adobe Photoshop CS4 Windows
File change date and time	23:54, 14 May 2012
Exposure Program	Aperture priority
Exif version	2.21
Date and time of digitizing	04:58, 11 May 2012
Shutter speed	12.965784
APEX aperture	4
Exposure bias	−1
Maximum land aperture	3 APEX (f/2.83)
Metering mode	Pattern
Light source	Unknown
Flash	Flash did not fire
DateTime subseconds	27
DateTimeOriginal subseconds	27
DateTimeDigitized subseconds	27
Color space	sRGB
Sensing method	One-chip color area sensor
File source	Digital still camera
Scene type	A directly photographed image
Custom image processing	Normal process
Exposure mode	Auto exposure
White balance	Auto white balance
Digital zoom ratio	1
Focal length in 35 mm film	270 mm
Scene capture type	Standard
Scene control	Low gain up
Contrast	Soft
Saturation	Normal
Sharpness	Normal
Subject distance range	Unknown
Subject distance	4,294,967,295 meters
Image width	4,288 px
Image height	2,848 px
Serial number of camera	6027263
Lens used	180.0 mm f/2.8
Date metadata was last modified	18:54, 14 May 2012
Rating (out of 5)	0
Unique ID of original document	322D51AD12DD5A40EA3B13CFB5901614
IIM version	61,839

File:ISS-31 Linear dunes in the Great Sand Sea in southwest Egypt.jpg

Summary

Licensing

Captions

Items portrayed in this file

depicts

significant event

Expedition 31

copyright status

public domain

inception

11 May 2012

captured with

Nikon D2Xs

catalog code

ISS031-E-030783

File history

File usage

Global file usage

Metadata